Anomalous crystallization mechanism in the synthesis of nanocrystalline ZSM-5

Nanocrystalline ZSM-5 (crystal size in the range 10-100 nm) has been synthesized in only 24 h by hydrothermal crystallization of clear supersaturated homogeneous synthesis mixtures. The influence of the aluminum source, aging time, pH, water content and presence of alkaline cations on the properties of the final nanocrystalline zeolite have been studied. Samples with different degrees of crystallinity have been prepared and characterized by X-ray fluorescence, X-ray diffraction, solid state MAS-NMR, transmission electron microscopy and nitrogen adsorption (BET) in order to investigate the crystallization mechanism. The process involves the formation of an initial amorphous solid prior to the zeolite crystallization, which is gradually transformed into nanocrystalline ZSM-5 through solid-solid transformations. Additionally, the conventional formation of ZSM-5 from crystalline nuclei generated in the remaining liquid solution is observed after 48 h. (C) 2000 Elsevier Science B.V. All rights reserved.